1. Field of the Invention
This invention relates to improvements in gate valves and more particularly, but not by way of limitation, to a gate valve having the sealing means disposed on the upstream side of the closure means.
2. Description of the Prior Art
Gate valves are in widespread use for providing a positive control of the flow of fluids through pipe lines, and the like. These valves are normally provided with a gate member which is interposed between the inlet and outlet ports of the valve, and which is reciprocal within the valve body to provide selective open and closed positions therefor. A valve seat is normally provided in the valve body for engagement with the gate member in the closed position of the valve for precluding leakage of fluid. The valve seat is usually disposed on the downstream side of the closure member, and in the closed position of the valve, the pressure of the fluid in the line bears against the closure member for urging the member tightly against the valve seat. Whereas this has been considered a desirable arrangement since the pressure of the fluid may increase the sealing pressure between the gate and the sealing members of the valve seat. However, under actual use conditions, it is frequently very difficult to open the valve since the great forces on the gate member must be overcome in order to raise the gate member from the closed position in the valve body. In order to alleviate this problem, a gate valve as shown in my prior U.S. Pat. No. 3,050,077, issued Aug. 21, 1962, and entitled "Double Sealed Gate Valve" was developed but the construction of this valve is complicated and expensive.